1. Field of the Invention
The present invention relates to a thin film transistor substrate and a display apparatus having the same, and more particularly to a thin film transistor substrate and a display apparatus using the thin film transistor substrate and having a pixel electrode on which a light emitting layer is formed.
2. Description of the Related Art
Today, OLED (organic light emitting diode) is a popular type of flat panel display that is especially appreciated for its low voltage-driving, light weight, slim shape, wide angular field, and quick response. OLED displays are generally classified into two categories depending on the driving method: a passive matrix and an active matrix. The passive matrix OLED is simple in its manufacturing process but has the disadvantage of dramatically increased power consumption with increases in the size of the display and the resolution. Due to this disadvantage, the use of passive matrix is somewhat limited to a small-sized display apparatuses. While the active matrix OLED is more useful for large displays and high resolution, its manufacturing process is more complicated.
A plurality of TFT transistors are provided on the OLED substrate to drive and an anode electrode forming a pixel and a cathode functioning as a reference voltage are formed on the TFT. When a voltage is applied to the two electrodes, an exciton is formed by combination of a hole and an electron. The exciton emits light in a light emitting layer interposed between the two electrodes. The OLED displays images by adjusting this emitted light.
A plurality of TFTs are formed on the OLED substrate. A switching transistor connected to a data line and a driving transistor connected to a voltage supply line form a pixel. A data line assembly metal layer is deposited and formed into a source electrode and a drain electrode. A plurality of contact holes are formed to connect wires when a plurality of TFTs are formed. However, these contact holes can be problematic when an etchant flows through the contact hole during processing and causes wire lifting.
Wire lifting poses a problem especially around a boundary area where a gate line assembly metal layer overlaps the data line assembly metal layer due to a height difference between the metal layers. A thin protective layer is formed at the boundary area. When the contact hole is formed on the thin protective layer, the wire lifting is largely induced by the etchant and it becomes difficult to apply a normal voltage to the pixel.